Useful methods for the evaluation of systems of insulation for random-wound stators of rotating electric machines are given. The chief purpose is to classify insulation systems in accordance with their temperature limits by test, rather than by chemical composition. The procedure is intended to evaluate insulation systems for use in usual service conditions with air cooling. It has also been a useful tool for evaluating systems for special requirements where machines are enclosed in gas atmospheres, subjected to strong chemicals, metal dusts, or submersion in liquids, although these special requirements are beyond the scope of this test procedure.

The chief purpose of this test procedure is to classify insulation systems in accordance with their temperature limits by test, rather than by chemical composition. The intention is, Þrst to classify according to the recognized thermal classiÞcation A, B, F, H, and above H categories as referenced in the Appendix. The motorette procedure is intended to be used as an Industry Standard for insulation systems in that data obtained in accordance with this standard can be correlated between testing laboratories. A wide variety of synthetic electrical insulation materials is available for application in electric machinery and apparatus. As there is a growing tendency either to rely solely on these materials as electrical insulation, or to employ them with the old familiar materials in novel combinations, there is a corresponding increase in the problems associated with the selection and evaluation of insulations. Consequently a complete insulation system must be evaluated rather than testing...